1. Technical Field
This invention relates generally to pulse width modulated power converters, and more specifically to a precision triangle waveform generator that generates a triangle wave used, for example, in interleaved pulse width modulation amplifiers.
2. Related Art
Pulse width modulation (PWM) amplification for audio applications has been used to increase efficiency by incorporating output devices that act as switches as opposed to linear devices that must dissipate a substantial amount of power. In PWM amplifiers, an audio input signal is converted to a pulse width modulated waveform. To this end, an audio signal is provided to the amplifier to modulate the width of a rectangular waveform based, for example, on the amplitude of the audio signal. The modulated waveform is used to drive one or more output devices as switches that are either fully saturated or off. The output devices, often implemented using switching power transistors, may be aligned in half-bridge pairs such that one device of the pair switches a positive voltage to the output, while the other device switches a negative voltage to the output. The switched output signals may be provided to the input of a low-pass filter in an attempt to remove harmonic signals and sidebands that are beyond the spectrum of the desired output waveform. The filtered analog signal is used to drive the load, such as a loudspeaker.
Triangle waveform generators are used to modulate the audio signal to generate the pulse width modulated waveforms. Such triangle waveform generators may employ voltage controlled oscillators whose frequency is responsive to a certain control voltage. The triangle wave generated by such a triangle waveform generator may be phase locked to a reference frequency. The triangle wave may be modulated by the control voltage to map the amplitude into pulse width. Presently, triangle waveform generators are not capable of concurrently controlling one or more of the wave amplitude, frequency, symmetry and/or phase. Thus, systems and methods to more accurately control the quality of the triangle waveform are needed.